<HTML>
<BODY BGCOLOR="white">
<PRE>
<FONT color="green">001</FONT>    // Copyright (c) 2011, Mike Samuel<a name="line.1"></a>
<FONT color="green">002</FONT>    // All rights reserved.<a name="line.2"></a>
<FONT color="green">003</FONT>    //<a name="line.3"></a>
<FONT color="green">004</FONT>    // Redistribution and use in source and binary forms, with or without<a name="line.4"></a>
<FONT color="green">005</FONT>    // modification, are permitted provided that the following conditions<a name="line.5"></a>
<FONT color="green">006</FONT>    // are met:<a name="line.6"></a>
<FONT color="green">007</FONT>    //<a name="line.7"></a>
<FONT color="green">008</FONT>    // Redistributions of source code must retain the above copyright<a name="line.8"></a>
<FONT color="green">009</FONT>    // notice, this list of conditions and the following disclaimer.<a name="line.9"></a>
<FONT color="green">010</FONT>    // Redistributions in binary form must reproduce the above copyright<a name="line.10"></a>
<FONT color="green">011</FONT>    // notice, this list of conditions and the following disclaimer in the<a name="line.11"></a>
<FONT color="green">012</FONT>    // documentation and/or other materials provided with the distribution.<a name="line.12"></a>
<FONT color="green">013</FONT>    // Neither the name of the OWASP nor the names of its contributors may<a name="line.13"></a>
<FONT color="green">014</FONT>    // be used to endorse or promote products derived from this software<a name="line.14"></a>
<FONT color="green">015</FONT>    // without specific prior written permission.<a name="line.15"></a>
<FONT color="green">016</FONT>    // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS<a name="line.16"></a>
<FONT color="green">017</FONT>    // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT<a name="line.17"></a>
<FONT color="green">018</FONT>    // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS<a name="line.18"></a>
<FONT color="green">019</FONT>    // FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE<a name="line.19"></a>
<FONT color="green">020</FONT>    // COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,<a name="line.20"></a>
<FONT color="green">021</FONT>    // INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,<a name="line.21"></a>
<FONT color="green">022</FONT>    // BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;<a name="line.22"></a>
<FONT color="green">023</FONT>    // LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER<a name="line.23"></a>
<FONT color="green">024</FONT>    // CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT<a name="line.24"></a>
<FONT color="green">025</FONT>    // LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN<a name="line.25"></a>
<FONT color="green">026</FONT>    // ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE<a name="line.26"></a>
<FONT color="green">027</FONT>    // POSSIBILITY OF SUCH DAMAGE.<a name="line.27"></a>
<FONT color="green">028</FONT>    <a name="line.28"></a>
<FONT color="green">029</FONT>    package org.owasp.html;<a name="line.29"></a>
<FONT color="green">030</FONT>    <a name="line.30"></a>
<FONT color="green">031</FONT>    import java.util.LinkedList;<a name="line.31"></a>
<FONT color="green">032</FONT>    import java.util.List;<a name="line.32"></a>
<FONT color="green">033</FONT>    import javax.annotation.Nullable;<a name="line.33"></a>
<FONT color="green">034</FONT>    <a name="line.34"></a>
<FONT color="green">035</FONT>    import com.google.common.collect.Lists;<a name="line.35"></a>
<FONT color="green">036</FONT>    <a name="line.36"></a>
<FONT color="green">037</FONT>    /**<a name="line.37"></a>
<FONT color="green">038</FONT>     * Consumes an HTML stream, and dispatches events to a policy object which<a name="line.38"></a>
<FONT color="green">039</FONT>     * decides which elements and attributes to allow.<a name="line.39"></a>
<FONT color="green">040</FONT>     */<a name="line.40"></a>
<FONT color="green">041</FONT>    public final class HtmlSanitizer {<a name="line.41"></a>
<FONT color="green">042</FONT>    <a name="line.42"></a>
<FONT color="green">043</FONT>      /**<a name="line.43"></a>
<FONT color="green">044</FONT>       * Receives events based on the HTML stream, and applies a policy to decide<a name="line.44"></a>
<FONT color="green">045</FONT>       * what HTML constructs to allow.<a name="line.45"></a>
<FONT color="green">046</FONT>       * Typically, implementations use an {@link HtmlStreamRenderer} to produce<a name="line.46"></a>
<FONT color="green">047</FONT>       * the sanitized output.<a name="line.47"></a>
<FONT color="green">048</FONT>       *<a name="line.48"></a>
<FONT color="green">049</FONT>       * &lt;p&gt;<a name="line.49"></a>
<FONT color="green">050</FONT>       * &lt;b&gt;Implementations of this class are in the TCB.&lt;/b&gt;&lt;/p&gt;<a name="line.50"></a>
<FONT color="green">051</FONT>       */<a name="line.51"></a>
<FONT color="green">052</FONT>      @TCB<a name="line.52"></a>
<FONT color="green">053</FONT>      public interface Policy extends HtmlStreamEventReceiver {<a name="line.53"></a>
<FONT color="green">054</FONT>        /**<a name="line.54"></a>
<FONT color="green">055</FONT>         * Called when an HTML tag like {@code &lt;foo bar=baz&gt;} is seen in the input.<a name="line.55"></a>
<FONT color="green">056</FONT>         *<a name="line.56"></a>
<FONT color="green">057</FONT>         * @param elementName a normalized (lower-case for non-namespaced names)<a name="line.57"></a>
<FONT color="green">058</FONT>         *     element name.<a name="line.58"></a>
<FONT color="green">059</FONT>         * @param attrs a list of alternating attribute name and value pairs.<a name="line.59"></a>
<FONT color="green">060</FONT>         *     For efficiency, this list may be mutated by this during this method<a name="line.60"></a>
<FONT color="green">061</FONT>         *     call, but ownership reverts to the caller on method exit.<a name="line.61"></a>
<FONT color="green">062</FONT>         *     The values are raw -- HTML entities have been decoded.<a name="line.62"></a>
<FONT color="green">063</FONT>         *     Specifically, implementations are allowed to use a list iterator<a name="line.63"></a>
<FONT color="green">064</FONT>         *     and remove all disallowed attributes, add necessary attributes, and<a name="line.64"></a>
<FONT color="green">065</FONT>         *     then pass the list to an {@link HtmlStreamRenderer}.<a name="line.65"></a>
<FONT color="green">066</FONT>         */<a name="line.66"></a>
<FONT color="green">067</FONT>        void openTag(String elementName, List&lt;String&gt; attrs);<a name="line.67"></a>
<FONT color="green">068</FONT>    <a name="line.68"></a>
<FONT color="green">069</FONT>        /**<a name="line.69"></a>
<FONT color="green">070</FONT>         * Called when an HTML tag like {@code &lt;/foo&gt;} is seen in the input.<a name="line.70"></a>
<FONT color="green">071</FONT>         *<a name="line.71"></a>
<FONT color="green">072</FONT>         * @param elementName a normalized (lower-case for non-namespaced names)<a name="line.72"></a>
<FONT color="green">073</FONT>         *     element name.<a name="line.73"></a>
<FONT color="green">074</FONT>         */<a name="line.74"></a>
<FONT color="green">075</FONT>        void closeTag(String elementName);<a name="line.75"></a>
<FONT color="green">076</FONT>    <a name="line.76"></a>
<FONT color="green">077</FONT>        /**<a name="line.77"></a>
<FONT color="green">078</FONT>         * Called when textual content is seen.<a name="line.78"></a>
<FONT color="green">079</FONT>         * @param textChunk raw content -- HTML entities have been decoded.<a name="line.79"></a>
<FONT color="green">080</FONT>         */<a name="line.80"></a>
<FONT color="green">081</FONT>        void text(String textChunk);<a name="line.81"></a>
<FONT color="green">082</FONT>      }<a name="line.82"></a>
<FONT color="green">083</FONT>    <a name="line.83"></a>
<FONT color="green">084</FONT>      /**<a name="line.84"></a>
<FONT color="green">085</FONT>       * Sanitizes the given HTML by applying the given policy to it.<a name="line.85"></a>
<FONT color="green">086</FONT>       *<a name="line.86"></a>
<FONT color="green">087</FONT>       * &lt;p&gt;<a name="line.87"></a>
<FONT color="green">088</FONT>       * This method is not in the TCB.<a name="line.88"></a>
<FONT color="green">089</FONT>       *<a name="line.89"></a>
<FONT color="green">090</FONT>       * &lt;p&gt;<a name="line.90"></a>
<FONT color="green">091</FONT>       * This method has no return value since policies are assumed to render things<a name="line.91"></a>
<FONT color="green">092</FONT>       * they accept and do nothing on things they reject.<a name="line.92"></a>
<FONT color="green">093</FONT>       * Use {@link HtmlStreamRenderer} to render content to an output buffer.<a name="line.93"></a>
<FONT color="green">094</FONT>       *<a name="line.94"></a>
<FONT color="green">095</FONT>       * @param html A snippet of HTML to sanitize.  {@code null} is treated as the<a name="line.95"></a>
<FONT color="green">096</FONT>       *     empty string and will not result in a {@code NullPointerException}.<a name="line.96"></a>
<FONT color="green">097</FONT>       * @param policy The Policy that will receive events based on the tokens in<a name="line.97"></a>
<FONT color="green">098</FONT>       *     HTML.  Typically, this policy ends up routing the events to an<a name="line.98"></a>
<FONT color="green">099</FONT>       *     {@link HtmlStreamRenderer} after filtering.<a name="line.99"></a>
<FONT color="green">100</FONT>       *     {@link HtmlPolicyBuilder} provides an easy way to create policies.<a name="line.100"></a>
<FONT color="green">101</FONT>       */<a name="line.101"></a>
<FONT color="green">102</FONT>      public static void sanitize(@Nullable String html, final Policy policy) {<a name="line.102"></a>
<FONT color="green">103</FONT>        if (html == null) { html = ""; }<a name="line.103"></a>
<FONT color="green">104</FONT>    <a name="line.104"></a>
<FONT color="green">105</FONT>        TagBalancingHtmlStreamEventReceiver balancer<a name="line.105"></a>
<FONT color="green">106</FONT>            = new TagBalancingHtmlStreamEventReceiver(policy);<a name="line.106"></a>
<FONT color="green">107</FONT>    <a name="line.107"></a>
<FONT color="green">108</FONT>        // According to Opera the maximum table nesting depth seen in the wild is<a name="line.108"></a>
<FONT color="green">109</FONT>        // 795, but 99.99% of documents have a table nesting depth of less than 22.<a name="line.109"></a>
<FONT color="green">110</FONT>        // Since each table has a nesting depth of 4 (incl. TBODY), this leads to a<a name="line.110"></a>
<FONT color="green">111</FONT>        // document depth of 90 (incl. HTML &amp; BODY).<a name="line.111"></a>
<FONT color="green">112</FONT>        // Obviously table nesting depth is not the same as whole document depth,<a name="line.112"></a>
<FONT color="green">113</FONT>        // but it is the best proxy I have available.<a name="line.113"></a>
<FONT color="green">114</FONT>        // See http://devfiles.myopera.com/articles/590/maxtabledepth-url.htm for<a name="line.114"></a>
<FONT color="green">115</FONT>        // the original data.<a name="line.115"></a>
<FONT color="green">116</FONT>    <a name="line.116"></a>
<FONT color="green">117</FONT>        // Webkit defines the maximum HTML parser tree depth as 512.<a name="line.117"></a>
<FONT color="green">118</FONT>        // http://trac.webkit.org/browser/trunk/Source/WebCore/page/Settings.h#L408<a name="line.118"></a>
<FONT color="green">119</FONT>        // static const unsigned defaultMaximumHTMLParserDOMTreeDepth = 512;<a name="line.119"></a>
<FONT color="green">120</FONT>    <a name="line.120"></a>
<FONT color="green">121</FONT>        // The first number gives us a lower bound on the nesting depth we allow,<a name="line.121"></a>
<FONT color="green">122</FONT>        // 90, and the second gives us an upper bound: 512.<a name="line.122"></a>
<FONT color="green">123</FONT>        // We do not want to bump right up against that limit.<a name="line.123"></a>
<FONT color="green">124</FONT>        // 256 is substantially larger than the lower bound and well clear of the<a name="line.124"></a>
<FONT color="green">125</FONT>        // upper bound.<a name="line.125"></a>
<FONT color="green">126</FONT>        balancer.setNestingLimit(256);<a name="line.126"></a>
<FONT color="green">127</FONT>    <a name="line.127"></a>
<FONT color="green">128</FONT>        balancer.openDocument();<a name="line.128"></a>
<FONT color="green">129</FONT>    <a name="line.129"></a>
<FONT color="green">130</FONT>        HtmlLexer lexer = new HtmlLexer(html);<a name="line.130"></a>
<FONT color="green">131</FONT>        // Use a linked list so that policies can use Iterator.remove() in an O(1)<a name="line.131"></a>
<FONT color="green">132</FONT>        // way.<a name="line.132"></a>
<FONT color="green">133</FONT>        LinkedList&lt;String&gt; attrs = Lists.newLinkedList();<a name="line.133"></a>
<FONT color="green">134</FONT>        while (lexer.hasNext()) {<a name="line.134"></a>
<FONT color="green">135</FONT>          HtmlToken token = lexer.next();<a name="line.135"></a>
<FONT color="green">136</FONT>          switch (token.type) {<a name="line.136"></a>
<FONT color="green">137</FONT>            case TEXT:<a name="line.137"></a>
<FONT color="green">138</FONT>              balancer.text(<a name="line.138"></a>
<FONT color="green">139</FONT>                  Encoding.decodeHtml(html.substring(token.start, token.end)));<a name="line.139"></a>
<FONT color="green">140</FONT>              break;<a name="line.140"></a>
<FONT color="green">141</FONT>            case UNESCAPED:<a name="line.141"></a>
<FONT color="green">142</FONT>              balancer.text(Encoding.stripBannedCodeunits(<a name="line.142"></a>
<FONT color="green">143</FONT>                  html.substring(token.start, token.end)));<a name="line.143"></a>
<FONT color="green">144</FONT>              break;<a name="line.144"></a>
<FONT color="green">145</FONT>            case TAGBEGIN:<a name="line.145"></a>
<FONT color="green">146</FONT>              if (html.charAt(token.start + 1) == '/') {  // A close tag.<a name="line.146"></a>
<FONT color="green">147</FONT>                balancer.closeTag(HtmlLexer.canonicalName(<a name="line.147"></a>
<FONT color="green">148</FONT>                    html.substring(token.start + 2, token.end)));<a name="line.148"></a>
<FONT color="green">149</FONT>                while (lexer.hasNext()<a name="line.149"></a>
<FONT color="green">150</FONT>                       &amp;&amp; lexer.next().type != HtmlTokenType.TAGEND) {<a name="line.150"></a>
<FONT color="green">151</FONT>                  // skip tokens until we see a "&gt;"<a name="line.151"></a>
<FONT color="green">152</FONT>                }<a name="line.152"></a>
<FONT color="green">153</FONT>              } else {<a name="line.153"></a>
<FONT color="green">154</FONT>                attrs.clear();<a name="line.154"></a>
<FONT color="green">155</FONT>    <a name="line.155"></a>
<FONT color="green">156</FONT>                boolean attrsReadyForName = true;<a name="line.156"></a>
<FONT color="green">157</FONT>                tagBody:<a name="line.157"></a>
<FONT color="green">158</FONT>                while (lexer.hasNext()) {<a name="line.158"></a>
<FONT color="green">159</FONT>                  HtmlToken tagBodyToken = lexer.next();<a name="line.159"></a>
<FONT color="green">160</FONT>                  switch (tagBodyToken.type) {<a name="line.160"></a>
<FONT color="green">161</FONT>                    case ATTRNAME:<a name="line.161"></a>
<FONT color="green">162</FONT>                      if (!attrsReadyForName) {<a name="line.162"></a>
<FONT color="green">163</FONT>                        // Last attribute added was valueless.<a name="line.163"></a>
<FONT color="green">164</FONT>                        attrs.add(attrs.getLast());<a name="line.164"></a>
<FONT color="green">165</FONT>                      } else {<a name="line.165"></a>
<FONT color="green">166</FONT>                        attrsReadyForName = false;<a name="line.166"></a>
<FONT color="green">167</FONT>                      }<a name="line.167"></a>
<FONT color="green">168</FONT>                      attrs.add(HtmlLexer.canonicalName(<a name="line.168"></a>
<FONT color="green">169</FONT>                          html.substring(tagBodyToken.start, tagBodyToken.end)));<a name="line.169"></a>
<FONT color="green">170</FONT>                      break;<a name="line.170"></a>
<FONT color="green">171</FONT>                    case ATTRVALUE:<a name="line.171"></a>
<FONT color="green">172</FONT>                      attrs.add(Encoding.decodeHtml(stripQuotes(<a name="line.172"></a>
<FONT color="green">173</FONT>                          html.substring(tagBodyToken.start, tagBodyToken.end))));<a name="line.173"></a>
<FONT color="green">174</FONT>                      attrsReadyForName = true;<a name="line.174"></a>
<FONT color="green">175</FONT>                      break;<a name="line.175"></a>
<FONT color="green">176</FONT>                    case TAGEND:<a name="line.176"></a>
<FONT color="green">177</FONT>                      break tagBody;<a name="line.177"></a>
<FONT color="green">178</FONT>                    default:<a name="line.178"></a>
<FONT color="green">179</FONT>                      // Just drop anything not recognized<a name="line.179"></a>
<FONT color="green">180</FONT>                  }<a name="line.180"></a>
<FONT color="green">181</FONT>                }<a name="line.181"></a>
<FONT color="green">182</FONT>                if (!attrsReadyForName) {<a name="line.182"></a>
<FONT color="green">183</FONT>                  attrs.add(attrs.getLast());<a name="line.183"></a>
<FONT color="green">184</FONT>                }<a name="line.184"></a>
<FONT color="green">185</FONT>                balancer.openTag(<a name="line.185"></a>
<FONT color="green">186</FONT>                    HtmlLexer.canonicalName(<a name="line.186"></a>
<FONT color="green">187</FONT>                        html.substring(token.start + 1, token.end)),<a name="line.187"></a>
<FONT color="green">188</FONT>                    attrs);<a name="line.188"></a>
<FONT color="green">189</FONT>              }<a name="line.189"></a>
<FONT color="green">190</FONT>              break;<a name="line.190"></a>
<FONT color="green">191</FONT>            default:<a name="line.191"></a>
<FONT color="green">192</FONT>              // Ignore comments, XML prologues, processing instructions, and other<a name="line.192"></a>
<FONT color="green">193</FONT>              // stuff that shouldn't show up in the output.<a name="line.193"></a>
<FONT color="green">194</FONT>              break;<a name="line.194"></a>
<FONT color="green">195</FONT>          }<a name="line.195"></a>
<FONT color="green">196</FONT>        }<a name="line.196"></a>
<FONT color="green">197</FONT>    <a name="line.197"></a>
<FONT color="green">198</FONT>        balancer.closeDocument();<a name="line.198"></a>
<FONT color="green">199</FONT>      }<a name="line.199"></a>
<FONT color="green">200</FONT>    <a name="line.200"></a>
<FONT color="green">201</FONT>      private static String stripQuotes(String encodedAttributeValue) {<a name="line.201"></a>
<FONT color="green">202</FONT>        int n = encodedAttributeValue.length();<a name="line.202"></a>
<FONT color="green">203</FONT>        if (n &gt; 0) {<a name="line.203"></a>
<FONT color="green">204</FONT>          char last = encodedAttributeValue.charAt(n - 1);<a name="line.204"></a>
<FONT color="green">205</FONT>          if (last == '"' || last == '\'') {<a name="line.205"></a>
<FONT color="green">206</FONT>            int start = 0;<a name="line.206"></a>
<FONT color="green">207</FONT>            if (n != 1 &amp;&amp; last == encodedAttributeValue.charAt(0)) {<a name="line.207"></a>
<FONT color="green">208</FONT>              start = 1;<a name="line.208"></a>
<FONT color="green">209</FONT>            } else {<a name="line.209"></a>
<FONT color="green">210</FONT>              // Browsers deal with missing left quotes : &lt;img src=foo.png"&gt;<a name="line.210"></a>
<FONT color="green">211</FONT>              // but generally do not deal with missing right : &lt;img src="foo.png&gt;<a name="line.211"></a>
<FONT color="green">212</FONT>            }<a name="line.212"></a>
<FONT color="green">213</FONT>            return encodedAttributeValue.substring(start, n - 1);<a name="line.213"></a>
<FONT color="green">214</FONT>          }<a name="line.214"></a>
<FONT color="green">215</FONT>        }<a name="line.215"></a>
<FONT color="green">216</FONT>        return encodedAttributeValue;<a name="line.216"></a>
<FONT color="green">217</FONT>      }<a name="line.217"></a>
<FONT color="green">218</FONT>    <a name="line.218"></a>
<FONT color="green">219</FONT>    }<a name="line.219"></a>




























































</PRE>
</BODY>
</HTML>
